Recently, there has been increasing interests in antifouling materials for use in various biomedical applications. Fouling is an undesired process in which molecules and/or living organisms from environment attach and accumulate onto a surface. The undesired surface adsorption of biomacromolecules for example, can cause the failure of biomedical devices. Thus, materials with superior antifouling properties have been urgently sought.
In recent years, zwitterionic materials, especially carboxybetaine (CB)-based materials, have attracted great attention due to their outstanding antifouling properties, as well as the capability of further functionalization for biosensing and drug delivery. These materials have been proven to effectively reduce bacterial attachment, biofilm formation, and highly resist nonspecific protein adsorption even from undiluted blood plasma.
These zwitterionic coatings can reduce initial attachment and delay biofilm formation on surfaces, but they are not able to kill attached microorganisms. Pathogenic microbes are sometimes introduced into the patient during implantation operations and catheter insertions, causing the failure of implanted devices are necessary to antimicrobial agents to eliminate these microbes. Surface-responsive materials with antimicrobial properties have been developed for a broad spectrum of applications, but there has been a need for materials and coatings having both antimicrobial and antifouling/biocompatibility capabilities.
To address this issue, a cationic derivative of pCBMA was developed. A surface coated with the cationic derivative of pCBMA is able to catch and kill bacterial cells, switch to a zwitterionic antifouling surface, and release killed bacterial cells upon its hydrolysis. However, it was found that this material can only switch once from antimicrobial state to antifouling state and the process is not reversible. Moreover, the alcohol leaving groups also may not be suitable for applications which require that no small molecules to be leaked out. Therefore, a material that can reversibly switch between an antifouling surface and an antimicrobial surface is highly desired.
Hydrogels, which can trap water molecules inside their three-dimensional network, have been widely used as wound dressings, drug delivery carriers, tissue engineering scaffolds, and coatings for implantable biosensor. Zwitterionic material-based hydrogels have attracted notable attention due to their ultralow fouling properties described above, good biocompatibility and high water content. However, the potential biomedical applications of zwitterionic hydrogels have been limited by their low mechanical strength, among other things. Although the mechanical strength can be improved through the blending or co-polymerization of the zwitterionic monomers with other materials, such as 2-hydroxyethyl methacrylate) (HEMA) and N-isopropylacrylamide (NIPAm), the antifouling properties of these zwitterionic monomers are very often compromised.
Another problem with existing zwitterionic materials is that they are relatively fragile and not stretchable. This significantly limits their utility for flexible medical devices (such as heart valve, implantable biosensors, and tissue scaffolds) which require implanted materials to be elastic and fouling-resistant. The current hydrophobic elastic materials cannot resist bacterial attachment.
Accordingly, what is needed in the art is zwitterionic material integrating all desired and tunable properties including excellent antifouling property to prolong the lifetime of implanted materials, antimicrobial property to eliminate surgical infection and chronic inflammation, and good mechanical properties/stability to avoid the structure failure of the implanted material.